Optical systems are presently being employed in the communication of voice and video information as well as in the high speed transmission of data. Optical communication systems are desired because of the wide bandwidths available for the information signal channels. However, the available wide bandwidths for the signal content also permits noise to be present over the same wide bandwidths so that both the desired signals and the undesired noise is amplified by the optical system amplifiers.
This problem presently exists in fiber optic systems, and a number of Erbium doped fiber optic amplifier systems have been proposed for use with narrow bandwidth optical filters to reduce detected spontaneous--spontaneous beat noise. It also is desired to remove excess spontaneous emission in optical amplifier systems that utilize cascaded Erbium doped amplifiers in order to prevent premature amplifier saturation which results from amplification of the desired optical signals along with the spontaneous emission. It is further desired to provide an Erbium fiber optic amplifier which can be readily integrated with an optical filter to remove the undesired emissions.